Reactors and piping where reactions are required to be conducted at high temperature such as a synthesis gas production apparatus for producing synthesis gas by using natural gas as raw material are provided with coating as a refractory material on the inner surfaces thereof. Castable is often employed as a refractory material because it can be provided with ease. In many cases, castable contains sulfur compounds to a small extent and the sulfur compounds are released when it is exposed to high temperatures. Then, the released sulfur compounds can adversely affect the downstream apparatus and the products.
In the process of producing synthetic hydrocarbons such as naphtha, kerosene and gas oil by way of chemical reactions, in which natural gas is used as raw material, generally synthesis gas (mixture gas of carbon monoxide and hydrogen) is produced as an intermediate by a reforming reaction.
When producing synthesis gas, firstly the sulfur compounds contained in the natural gas to be used as raw material are removed in a desulfurization unit. Then, steam and/or carbon dioxide is added to the desulfurized natural gas and subsequently the desulfurized natural gas is introduced into a synthesis gas production apparatus and heated in a reformer. As a result, a reforming reaction proceeds in the reformer due to a catalysis of the reforming catalyst filled in the reformer to thereby produce synthesis gas. While a steam reforming method using steam is mainly employed for the reforming reaction, a carbon dioxide reforming method using carbon dioxide has been put to practical use in recent years. A carbon dioxide reforming method does not require removal of the carbon dioxide contained in natural gas before a reforming reaction and hence provides an advantage of improving the efficiency of synthesis gas production process and reducing the cost. Furthermore, the unreacted carbon dioxide contained in the produced synthesis gas and the produced carbon dioxide can be separated and collected for recycling in the synthesis gas production process so as to be reused by the carbon dioxide reforming reaction. Thus, carbon dioxide can be highly efficiently exploited as resource.
Thereafter, typically, liquid hydrocarbons are produced from the produced synthesis gas by way of a Fischer-Tropsch reaction and synthetic hydrocarbons such as product fuel oil are produced by hydroprocessing the obtained liquid hydrocarbons in a hydrogenation process. The series of steps including a Fischer-Tropsch reaction is referred to as Gas-to-Liquids (GTL) process. Synthesis gas can also be used for methanol synthesis and oxo-synthesis.
Reforming reactions proceed at high temperatures typically between 700 and 900° C. in the case of steam reforming method, for example. Therefore, the synthesis gas that is discharged from the exit of a reformer is fed to a waste heat boiler for a heat-exchange process by way of piping coated with refractory castable.